drainagezones

Drainage zones, also referred to as drainage areas or catchment zones, are geographic regions in which all precipitation and runoff drain toward a common outlet, such as a stream, river, lake, or coastal boundary. They are the functional units used in hydrology and water resources planning to study how water moves through a landscape.

Delimitation is typically based on topography and hydrology. Ridges and divides define zone boundaries, while stream networks indicate internal drainage partitioning. Modern delineation relies on digital elevation models (DEMs) and geographic information systems to trace flow directions and to produce nested hierarchies of zones, from large river basins to smaller sub-catchments.

Applications include flood forecasting and floodplain mapping, water balance and groundwater recharge studies, and ecological and land-use planning. In urban drainage, zones correspond to sewer or stormwater catchment areas, guiding design, maintenance, and pollutant load management.

Limitations and considerations: boundaries can change with land-use change, rainfall patterns, and climate change; data quality and resolution affect accuracy; zones are simplifications of complex hydrological processes.